Marseille successfully foiled Real until the Portugal winger inspired his side to three goals in six minutes early in the second half.
Ronaldo broke the deadlock in the 58th minute and was brought down for a penalty a minute later, when visiting defender Souleymane Diawara was sent off.
Kaka scored from the spot and Ronaldo bagged his second in the 64th to leave Real with two wins from two.
"The game was evenly-balanced for 45 minutes but we were clearly superior for the second 45 minutes," Real coach Manuel Pellegrini said.
Pellegrini sent out his big guns from the start with Kaka, Ronaldo and Benzema leading the line, but they saw little of the ball with his side struggling to find any rhythm early on.
Pellegrini looked a concerned figure on the edge of his technical area and the visitors carved the first clear opening when Mamadou Niang forced Iker Casillas to save in a one-on-one after 26 minutes.
Ronaldo raised the home crowd's spirits with a couple of long-range efforts, and then just before the interval, Kaka backheeled a ball through for Benzema who was denied by a smart save from Steve Mandanda.
The game exploded into life early in the second half with a classic bit of route-one football. Pepe's long ball out of defence sent Ronaldo scampering clear and he calmly put the ball underneath Mandanda.
DISPUTED PENALTY
With the crowd up a minute later, Ronaldo tore off down the left wing and evaded Gabriel Heinze only to be taken out by the covering Diawara as he cut into the area.
The Marseille defender was sent off and Kaka scored the penalty.
"It was a very harsh decision to give a penalty and then to send off our player. After the penalty the game was over for us," Marseille coach Didier Deschamps said.
"For one hour we played a good game and we had chances in the first half. I don't think the result was fair."
Pellegrini disputed Deschamps view of the penalty decision:
"I have seen the condition of Ronaldo's ankle and I don't think the referee got it wrong. We'll have to see whether he'll make it for the trip to Sevilla on Sunday.
The visitors barely had time to recover when Real sliced them open again. Benzema played a one-two with Kaka on the edge of the area and slipped the ball across the goal for Ronaldo to net at the far post.
Ronaldo was given a standing ovation as he left the pitch in the 70th minute, limping from Diawara's earlier challenge.
Marseille battled on with 10 men and Ezequiel Garay had to boot the ball off Real's line at the end, after Hatem Ben Arfa's cross-cum-shot hit the post, and rolled across the area.
